A concrete arch dam is used in sites where the ratio of width between abutments to height is not great and where the foundation at the abutments is solid rock capable of resisting great forces. The arch provides resistance to movement. When combined with the weight of concrete (arch-gravity dam), both the weight and shape of the structure provide great resistance to the pressure of water.

a dam that is curved inwards from the downstream side, or is convex from that point

a structure curving

A concrete or masonry dam which is curved in plan so to transmit the major part of the water load to the abutements.

Curved masonry or concrete dam, convex in shape upstream, that depends on arch action for its stability; the load or water pressure is transferred by the arch to the Abutments.

An arch dam is a thin, curved concrete or masonry dam structure which is curved upstream in plan so that the force of the water against it squeezes the arch, compressing and strengthening the structure and pushing it into the ground. An arch dam is most likely used in a narrow site in a mountainous area with steep walls of sound rock.